1. Technical Field
The present invention relates to a image forming apparatus, storage medium storing a program, digital data management system, and a method for acquiring a time stamp issued by a time stamp station for authentication of a time of generation of digital data.
2. Related Art
When digital data of an electronic document file, etc. are generated in a computer, the time of generation (hereinafter called generation time) is generally set by a system as the attribute information about the digital data. Although the generation time is normally considered attribute information which should not be changed, in practice it can be rewritten like general data. That is, since digital data can be freely generated as data having a past or future time, when the digital data were generated cannot be confirmed by reference to only the attribute information.
Presently, a time stamp station of a third party is provided in order to authenticate the generation time of digital data. That is, when a user transmits to the time stamp station a time stamp request including the digest (hash value) of the digital data, the time stamp station adds time information to the transmitted digest, places a digital signature by means of a private key of the time stamp station, and then returns the signed digest. The returned information is generally referred to as a “time stamp token”. When the user wishes to certify the presence of the digital data at a certain time, the user requests to verify the time stamp by transmitting to the time stamp station the digest with the time stamp of the digital data added thereto. Upon receipt of the request, the time stamp station verifies the transmitted time stamp by means of the digital signature. Thus, the user can certify that the digital data existed at the certain time.
A recent image forming apparatus such as a multi-functional device is loaded with a computer, and can process a large amount of various image data by virtue of including a facsimile function, a mail function, etc. in addition to a scan function and a copy function. The read image data tend to have the opportunity to be stored as digital data based on, for example, the e-Document Law put into effect on Apr. 1, 2005 in Japan. An image forming apparatus is basically not a device for accumulating and managing read data. Therefore, the image forming apparatus transmits read data to a document management server, etc. for management of a document through a network to separately manage the read data according to the operation of the document management system.
When an image acquired by the image forming apparatus is for example, a confidential document, the user may desire that the document be stored and managed after the above-mentioned time stamp is acquired and added to the document. In the conventional image forming apparatus, a time stamp is readily acquired after a confidential document is read, is added to the document and transmitted to the document management server.
However, in the image forming apparatus, acquiring a time stamp each time digital data is generated is not necessarily appropriate. For example, since a client terminal device formed by a general-purpose personal computer (PC), etc. is used privately, few problems are considered to occur when a time stamp is acquired each time digital data are generated with relationships with other users and processes taken into account. On the other hand, the image forming apparatus is shared among multiple users. Therefore, when digital data are generated by reading an image, a conventional image forming apparatus acquires a time stamp from a time stamp station and adds it to the digital data, and transmits the digital data with the time stamp added thereto to the document management server, thereby performing a series of data processing operations. That is, performing the series of processing operations each time the digital data is generated is not always appropriate, from the viewpoint of processing load, etc. Therefore, the image forming apparatus desirably has the ability to acquire a time stamp with appropriate timing.